[Qemu-devel] Re: [PATCH] Save 64-bit of the IA-32e capable sysenter MSRs

[Avi Kivity]

Alexander Graf wrote:
> Hi,
>
> When transitioning from KVM to the qemu userspace, we try to get and 
> push a whole bunch of MSR values, including the SYSENTER ones. While 
> this is basically a good idea, qemu doesn't know anything about 
> SYSENTER on x86_64, which is an additional feature only available on 
> Intel CPUs and thus defines SYSENTER_EIP and SYSENTER_ESP as 32-bit 
> values.
>
> Because we're saving/restoring the SYSENTER values on transitions to 
> userspace and the values in env->cpu only hold 32 bits, they get 
> truncated to 32-bit. The easiest way around this is to widen the 
> fields to 64 bits. This should not disturb the current functionality, 
> but allows us to run 32-bit code on x86_64 using VMX.
>
> As this is KVM specific for now, I'll only CC the qemu mailinglist, 
> but wouldn't encourage qemu to take the patch for now, as it's not 
> necessary when emulating an AMD CPU.

Applied, thanks.  I imagine save/restore support needs updating as 
well?  That should go into qemuy btw since maintaining the save/restore 
format across forks isn't possible.

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